Implementation of a communication link in powered device for layer 2 support

ABSTRACT

A system and method for enabling communication between power source equipment and a powered device chip. In one embodiment, communication between the power source equipment and the powered device chip is enabled through a communication link established between the powered device chip and a host device on the powered device.

BACKGROUND

1. Field of the Invention

The present invention relates generally to Power over Ethernet (PoE)and, more particularly, to the implementation of a communication link ina powered device to further enhance Layer 2 support concepts such asthose set forth by the IEEE802.3af Task Force.

2. Introduction

The IEEE 802.3af PoE standard provides a framework for delivery of powerfrom power source equipment (PSE) to a powered device (PD) over Ethernetcabling. In this PoE process, a valid device detection is firstperformed. This detection process identifies whether or not it isconnected to a valid device to ensure that power is not applied tonon-PoE capable devices.

After a valid PD is discovered, the PSE can optionally perform a powerclassification. IEEE 802.3af defines five power classes for a PD device.The completion of this power classification process enables the PSE tomanage the power that is delivered to the various PDs connected to thePSE. If a particular power class is identified for a particular PD, thenthe PSE can allocate the appropriate power for that PD.

Once the power is connected to the device, the PSE uses either AC or DCDisconnect method to find out whether or not the device is stillconnected. In the DC disconnect method, the PSE detects that the PD loadcurrent has dropped down to a certain value to conclude that the devicehas been disconnected. In the AC disconnect method, the PD disconnect isexamined by the AC impedance of the PD by the PSE, which is accomplishedby sending an AC probing signal. Monitoring the occurrence of adisconnect condition is crucial to ensuring that power delivery is alsodiscontinued over that Ethernet line.

As this PD connection and disconnection process illustrates, thedetection of a condition of a PD is crucial. In general, this reflectsthe importance of the PSE being aware of an operating condition of PDs.What is needed in this context is a mechanism that enhances the PSE'svisibility into the state or condition of operation of a connected PD.

SUMMARY

A system and/or method for implementation of a communication link inpowered device for layer 2 support, substantially as shown in and/ordescribed in connection with at least one of the figures, as set forthmore completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

FIG. 1 illustrates an embodiment of a powered device having acommunication interface to a powered device chip.

FIG. 2 illustrates a flowchart of a process of receiving informationfrom a powered device.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

The IEEE 802.3af Power over Ethernet (PoE) standard outlines a processby which power source equipment (PSE) can detect, classify, and allocatepower to powered devices (PDs) that are connected to the PSE viaEthernet cable. In the PoE detection process it is crucial to ensurethat power is only allocated to appropriately configured devices. Thisdetection process also prevents non-PoE devices from being damaged bythe PSE's 48V output. Proper detection of PDs is crucial for all otheraspects of a PSE's function.

FIG. 1 illustrates an embodiment of a PD chip 110 that can beincorporated in a media endpoint device (e.g., Internet Protocol phone,wireless access point, etc.) or network connectivity device (e.g.,switch). In the illustrated embodiment, the PD is designed to sourcepower through the data lines. Specifically, the PD sources power throughthe center tap of data transformers 102.

As further illustrated, PD chip 110 includes a detection switch 118 thatcontrols when the signature 25 kΩ resistance is applied as a load acrossthe line. In this detection stage, the PSE typically outputs a currentlimited detection voltage in the range of 2.5V to 10V. If the PSEdetects the proper signature resistance, then it is determined that aproper PD is at the end of the link.

The PSE then proceeds to the classification step. While theclassification step is optional, customers may well expectclassification because unclassified devices would unnecessarily wastepower and capacity of the PSE.

In the classification step, the PSE applies more voltage (up to 20.5V)to the link, and measures the current drawn by classification element116 between the 15.5V-20.5V range to determine the classification of thePD. Table 1 below shows the five PD classes identified in the 802.3afstandard. Future standards such as 802.3 at will feature a greaternumber of defined PD classes.

TABLE 1 Class Usage Min Power Output by PSE Max Power Input at PD 0Default 15.4 W 0.44 to 12.95 W 1 Optional  4.0 W  0.44 to 3.84 W 2Optional  7.0 W  3.84 to 6.49 W 3 Optional 15.4 W 6.49 to 12.95 W 4Reserved Act as Class 0 Reserved

Once the PSE has classified the PD, the PD is then supplied with fulloperating voltage. Under-voltage lockout (UVLO) element 114 is includedin PD chip 110 in part due to the length of cabling (e.g., 100 meters)over which power may be supplied. UVLO element 114 ensures that thevoltage at the PD is high enough such that the voltage will not dropbelow the minimum working voltage when load current is drawn from thecable. This prevents the pulse width modulation (PWM) DC:DC controller119 from starting up and shutting down repeatedly as power is initiallyapplied to the link. UVLO element 114 also ensures that the PWMcontroller 119 does not operate during the detection and classificationstages.

PWM controller 119 controls the operation of power field effecttransistor (FET) 140, which provides usable power to the PD once thefull operating voltage, for the detected or default PD class, is appliedto the line by the PSE. In the embodiment of FIG. 1, FET 140 isillustrated as being separate from PWM controller 119. In an alternativeembodiment, FET 140 is integrated with PWM controller 119.

Once the PD is powered, the PSE is designed to sense when a PD isdisconnected. This disconnect detection enables the PSE to power downthe link immediately. The PSE can also be designed to protect the cableand the PD from overcurrent and short-circuit conditions.

During the operation of the PD under power, PD chip 110 can be designedto monitor the operating condition or state of the power delivery to thePD. For example, PD chip 110 can be designed to monitor power deliveryparameters such as the actual power consumption of the PD, the currentpassed through to the PD, the chip or die temperature, and the powerclassification. PD chip 110 can also be designed to monitor theoperation of PD chip 110 during detection, classification, and poweringstages. Here, anomalous operating conditions, error conditions (e.g.,comparison of actual power versus allocated power), or other violationscan be detected by PD chip 110.

These various types of information that are generated by PD chip 110 areuseful in monitoring and controlling the overall operation of powerdelivery from the PSE to the PD. This information can be useful to thePSE itself in controlling the delivery of power to a particular PSE, orto an administrator that is overseeing the operation of the variousdeployed PDs.

Access to the information that can be provided by PD chip 110 istherefore a crucial aspect of general PoE network administration.Identifying an efficient mechanism for such communication is therefore akey. One communication option would require the inclusion of elementswithin PD chip 110 that could support direct communication between PDchip 110 and the PHY or host chip (e.g., enterprise IP phone chip). Withthis communication link between PD and PHY or host chip, the IP phones,Wireless Access Points, etc. using such a PD chip can send thisadditional information over Layer 2 which then can be used by the PSE.In general, Layer 1 communication using PD chip 110 would be expensive,have a slower response time, and suffer from relative inaccuracies.Moreover, some information that is generated by PD chip 110 could not becommunicated over a Layer 1 protocol.

It is therefore a feature of the present invention that operation andstatus information generated by PD chip 110 can be communicated to thePSE using an inexpensive communication mechanism. This inexpensivecommunication mechanism is based on Layer 2 communication between the PDand the PSE. Significantly, this Layer 2 communication is enabled viaexisting functionality that resides outside of PD chip 110.

To illustrate this feature of the present invention, reference is madeagain to the example embodiment illustrated in FIG. 1. As is furtherillustrated, PD chip 110 also includes a digital communication component112 that interfaces with communication link 130. Communication link 130is also connected to host chip 120. In one embodiment, communicationlink 130 is a serial communication link that can be enabled by suchtechnologies as I2C, SBI, UART, or the like.

Communication link 130 enables PD chip 110 to transmit operation andstatus information to host chip 120. In various embodiments, host chip120 can be embodied as a microcontroller, a PHY, a switching chip, anenterprise Internet Protocol phone chip, a wireless access point chip,or the like. The operation and status information would then betransmitted by host chip 120 to the PSE via a PHY transceiver or thelike. It should also be noted that PD chip 110 could also be designed tocommunicate information directly to the PHY transceiver or the host chipfor delivery to the PSE. In various embodiments, the Layer 2communication between host chip 120 and the PSE is a Layer 2communication that can be enabled by the Link Layer DiscoveryProtocol-Media Endpoint Discover (LLDP-MED), IEEE 802.1 ab Operation,Administration and Maintenance (OAM), or the like.

As communication link 130 is a bi-directional transmission channel,communication link 130 can also enable host chip 120 to send informationto PD chip 110 for various configuration purposes. For example, hostchip 120 can send information to PD chip 110 that can be used by PD chip110 for power limiting, power scaling, etc.

In general, communication link 130 enables the addition of intelligenceinto PD chip 110. In conventional systems, PD chip 110 would onlyrespond to PSE signal probes. The extent of that form of PD chipcommunication would be in the line signal characteristics that aremeasured by the PSE. Thus, it is a feature of the present invention thatPD chip 110 can now communicate with the PSE as part of a generalquery/response protocol. While details of this query/response protocolwould be implementation specific, the protocol would enable PD chip 110to intelligently respond to requests that are sent by the PSE. This formof intelligence in PD chip 110 enables the PD to operate in newcapacities in monitoring, configuration, and management of the PoEnetwork.

To illustrate an example of the use of the intelligence in PD chip 110,reference is now made to the flowchart of FIG. 2. As illustrated, theflowchart of FIG. 2 begins at step 202 where the PSE detects the PD. Asnoted above, this detection process is enabled using a 25 kΩ resistor,which is applied as a load across the line based upon the activation ofdetection switch 118 of PD chip 118. The PD is detected by the PSE oncethe PSE detects the proper signature impedance.

After the PSE detects the PD, the PSE, at step 204, then identifies theclassification of the PD. In the classification step, the PSE measuresthe current drawn by classification element 116 of PD chip 110 when thevoltage output by the PSE is between the 15.5V-20.5V range. The responsemeasured by the PSE is used to classify the PD, for example, inaccordance with the five PD classes specified by the 802.3af standard.Based on this determined classification, the PSE, at step 206, thenallocates power to the PD.

It is at this point in the process that the initial Layer 1configuration is established between the PSE and PD chip 110. The PSEwould then monitor the connection to determine when the PD has beendisconnected.

It is a feature of the present invention that further communications canalso be enabled between the PSE and host chip 120 to support Layer 2communications, which communications would supplement the Layer 1communications of steps 202-206. In the illustrated embodiment of FIG.1, digital communications component 112 can be designed to transmitoperation and/or status information that is generated by or otherwiseresident within PD chip 110. This transmission to host chip 120 occursat step 208 and is enabled through communication link 130.

Next, at step 210, host chip 120 forwards the received operation and/orstatus information to the PSE. This transmission is enabled via theexisting Layer 2 communication that is supported by host chip 120. Inthis manner, PD chip 110 leverages existing communication functionalitywithin the PD.

At step 212, the information received by the PSE from host chip 120 canbe used for any monitoring, configuration, or management purpose by thePSE or any other element that gains access to the information. As wouldbe appreciated, the particular use of the received information would beimplementation dependent.

To illustrate the potential value of this received information, considerthe following example that relates to PD classification. In this case,the information that is received by the PSE could be the actualclassification for which the PD was designed. Here, this actualclassification information could be received by the PSE and used as acheck to ensure that the initial classification identified by the PSE isaccurate. This augmented classification process would ensure thatinaccurate classifications, or default classifications, would becorrected based upon a PD's own accurate classification. Also, thisclassification information can have greater levels of granularity. Infact, the use of Layer 2 communication as part of the configurationprocess could obviate the need for the use of the optionalclassification step by the PSE. Here, a default classification could beused initially and changed upon receipt of the accurate classificationinformation via the Layer 2 communication.

In another example, the received information could be used simply tomonitor the operation of PD chip 110. Here, PD chip 110 can be designedto forward information related to any operating aspect of its components(e.g., current drawn, temperature, etc.). This information can be used,for example, to monitor whether dangerous operating conditions arepresent on the PD location.

As noted above, communication link 130 is a bi-directional communicationchannel. As such, communication link 130 can also be used to forwardinformation from PD chip 110 to host chip 120 as well as from host chip120 to PD chip 110. In the latter context, the information forwardedfrom host chip 120 to PD chip 110 can be used for configuration purposesor as part of a more general query/response protocol. For example, inthe context of the process of FIG. 2, the forwarding of information byPD chip 110 to host chip 120 in step 208 can be in response to aprevious request sent by the PSE (e.g., request for accurateclassification information). In another example, the information sent bythe PSE to PD chip 110 via host chip 120 can be used to configure orotherwise modify an aspect of operation of PD chip 110 (e.g., powerlimiting, power scaling, etc.)

These and other aspects of the present invention will become apparent tothose skilled in the art by a review of the preceding detaileddescription. Although a number of salient features of the presentinvention have been described above, the invention is capable of otherembodiments and of being practiced and carried out in various ways thatwould be apparent to one of ordinary skill in the art after reading thedisclosed invention, therefore the above description should not beconsidered to be exclusive of these other embodiments. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting.

1. A powered device that receives power over a network cable thatcouples said powered device to a power source equipment, comprising: aphysical layer communication component that enables data communicationbetween said powered device and said power source equipment, saidphysical layer communication component being coupled to said networkcable via data transformers; a powered device chip that is coupled tosaid network cable via said data transformers, said powered device chipincluding signature detection components that enable detection of saidpowered device by said power source equipment, and a power controllerthat controls power delivered by a field effect transistor to a load onsaid powered device; a host module that is coupled to said physicallayer communication component, said host module being configured tosupport a Layer 2 communication protocol between said host module andsaid power source equipment; and a communication link that connects saidpowered device chip to said host module, said communication linkenabling operation information from said powered device chip to betransmitted to said host module for communication of said operationinformation by said host module to said power source equipment via saidLayer 2 communication protocol.
 2. The powered device of claim 1,wherein said signature detection components are coupled to a 25 kΩresistor.
 3. The powered device of claim 1, wherein said powered devicechip further includes power classification components that enables saidpower source equipment to determine a power classification of thepowered device.
 4. The powered device of claim 1, wherein said powercontroller is a pulse width modulation controller.
 5. The powered deviceof claim 1, wherein said field effect transistor is external to saidpowered device chip.
 6. The powered device of claim 1, wherein saidfield effect transistor is incorporated in said powered device chip. 7.The powered device of claim 1, wherein said powered device chip conformsto IEEE 802.3af.
 8. The powered device of claim 1, wherein said hostmodule is one of a microcontroller, a PHY chip, a switching chip, anInternet Protocol phone chip, and a wireless access point chip.
 9. Thepowered device of claim 1, wherein said communication link is a seriallink.
 10. The powered device of claim 1, wherein said Layer 2communication protocol is a Link Layer Discovery Protocol-Media EndpointDiscover.
 11. The powered device of claim 1, wherein said Layer 2communication protocol is 802.1AB operations, administration, andmaintenance.
 12. The powered device of claim 1, wherein said operationinformation is one of actual power consumption, current, temperature,power class, and status reporting information.
 13. The powered device ofclaim 1, wherein said communication link enables said power sourceequipment to send a query to said powered device, and to return aresponse to said query from said powered device.
 14. A powered devicethat receives power over a network cable that couples said powereddevice to a power source equipment, comprising: a physical layercommunication component that enables data communication between saidpowered device and said power source equipment, said physical layercommunication component being coupled to said network cable via datatransformers; a powered device chip that is coupled to said networkcable via said data transformers, said powered device chip includingsignature detection components that enable detection of said powereddevice by said power source equipment, and a power controller thatcontrols power delivered by a field effect transistor to a load on saidpowered device; a communication link that connects said powered devicechip to a host module, said host module coupled to said physical layercommunication component and being configured to support a Layer 2communication protocol between said host module and said power sourceequipment, wherein said communication link enables operation informationfrom said powered device chip to be transmitted to said host module forcommunication of said operation information by said host module to saidpower source equipment via said Layer 2 communication protocol.
 15. Apowered device that receives power over a network cable that couplessaid powered device to a power source equipment, comprising: a physicallayer communication component that enables data communication betweensaid powered device and said power source equipment, said physical layercommunication component being coupled to said network cable via datatransformers; a powered device chip that is coupled to said networkcable via said data transformers, said powered device chip includingsignature detection components that enable detection of said powereddevice by said power source equipment, and a power controller thatcontrols power delivered by a field effect transistor to a load on saidpowered device; a communication link that connects said powered devicechip to a host module, said host module coupled to said physical layercommunication component and being configured to support a Layer 2communication protocol between said host module and said power sourceequipment, wherein said communication link enables a forwarding of arequest for operation information from said host module to said powereddevice, said request for operation information being received by saidhost module from said power source equipment via said physical layercommunication component.
 16. The powered device of claim 15, whereinsaid communication link is a serial link.
 17. The powered device ofclaim 15, wherein said Layer 2 communication protocol is a Link LayerDiscovery Protocol-Media Endpoint Discover.
 18. The powered device ofclaim 15, wherein said Layer 2 communication protocol is 802.1ABoperations, administration, and maintenance.
 19. The powered device ofclaim 15, wherein said operation information is one of actual powerconsumption, current, temperature, power class, and status reportinginformation.
 20. The powered device of claim 15, wherein said hostmodule is one of a microcontroller, a PHY chip, a switching chip, anInternet Protocol phone chip, and a wireless access point chip.
 21. Amethod in a powered device that receives power over a network cable thatcouples said powered device to a power source equipment, said powereddevice including a powered device chip having signature detectioncomponents that enable detection of said powered device by said powersource equipment and a power controller that controls power delivered bya power transistor to a load on said powered device, comprising:forwarding operation information from said powered device chip to a hostmodule via a communication link that connects said powered device chipto said host module, said host module being coupled to a physical layercommunication component in said powered device that enables datacommunication between said powered device and said power sourceequipment; and transmitting said operation information from said hostmodule to said power source equipment using a Layer 2 communicationprotocol.
 22. The method of claim 21, wherein said host module is one ofa microcontroller, a PHY chip, a switching chip, an Internet Protocolphone chip, and a wireless access point chip.
 23. The method of claim21, wherein said communication link is a serial link.
 24. The method ofclaim 21, wherein said Layer 2 communication protocol is a Link LayerDiscovery Protocol-Media Endpoint Discover.
 25. The method of claim 21,wherein said Layer 2 communication protocol is 802.1AB operations,administration, and maintenance.
 26. The method of claim 21, whereinsaid operation information is one of actual power consumption, current,temperature, power class, and status reporting information.